GST Calculator

How is GST calculated in Australia?

GST (Goods and Services Tax) in Australia is a flat 10% tax on most goods and services. There are two directions:

Adding GST: Net amount × 1.1 = GST-inclusive price
Removing GST: GST-inclusive amount ÷ 11 = GST component

The second formula is where most mistakes happen. Dividing by 11 is not the same as multiplying by 10%. A $110 invoice contains $10 of GST (110 ÷ 11), not $11 (110 × 10%). This single error, applied across a quarter of supplier invoices, overstates input tax credits on the BAS and creates a reconciliation gap with the ATO. The calculator above handles both directions automatically.

GST calculation examples

Adding GST to a $2,500 subcontractor quote

A plumber quotes $2,500 ex-GST for pipework on a construction site.

• GST: $2,500 × 0.10 = $250
• GST-inclusive price: $2,500 + $250 = $2,750

The $250 GST is what you claim back as an input tax credit on your BAS, assuming you hold a valid tax invoice and the expense is for business purposes.

Removing GST from a $4,400 supplier invoice

A freight company invoices $4,400 including GST for a domestic shipment.

• GST component: $4,400 ÷ 11 = $400
• Net amount: $4,400 − $400 = $4,000

When coding this in Xero or MYOB, the $4,000 goes to the freight expense account and the $400 to the GST paid account.

Mixed invoice with GST-free and taxable items

A supplier invoice for $3,300 includes $2,200 of taxable goods (GST-inclusive) and $1,100 of GST-free medical supplies.

• GST on taxable portion: $2,200 ÷ 11 = $200
• GST on GST-free portion: $0
• Total GST claimable: $200

This is why GST must be applied at the line level, not the invoice level. Applying 10% to the full $3,300 would claim $300 — overstating the credit by $100. For businesses processing high volumes of mixed-supply invoices, GST coding errors compound into material BAS inaccuracies over a reporting period.

How to use this GST calculator

1. Select Add GST if you have an ex-GST (net) amount and need the GST-inclusive price for your invoice.
2. Select Remove GST if you have a GST-inclusive amount from a supplier invoice and need to split it into net and GST for your accounts.
3. Enter the dollar amount — results appear instantly showing gross, net, and GST.
4. Use the GST figure when coding the transaction in your accounting software, and reconcile it against your BAS worksheet at the end of each period.

What items are GST-free in Australia?

Not all goods and services attract GST. The classification of each line item on a supplier invoice determines whether you can claim an input tax credit on your BAS.

GST-free supplies (0% GST, but you can still claim input tax credits on related business costs):

• Most basic food (unprocessed meat, fruit, vegetables, bread, milk)
• Medical and health services
• Educational courses
• Exports of goods and services
• International freight and transport
• Precious metals (gold, silver, platinum)
• Sales of going concerns

Input-taxed supplies (no GST charged, and no input tax credits claimable on related costs):

• Residential rent
• Most financial services (bank fees, loan interest)
• Sale of existing residential premises

The distinction matters in AP. If a supplier incorrectly charges GST on a GST-free item and you claim the credit, the ATO may disallow the claim on review. The ATO's GST guide provides the full classification list.

Do I need to register for GST?

You must register if your annual GST turnover (gross income from taxable sales) is $75,000 or more, or $150,000 for non-profit organisations. Turnover is assessed on a rolling 12-month basis — past or projected. Sole traders, companies, partnerships, and trusts all face the same threshold.

Voluntary registration below the threshold can make sense if your customers are GST-registered businesses, as they can claim back the GST you charge. It also means you can claim input tax credits on your own business purchases. Register through the ATO's GST registration page.

How does GST work on imported goods?

Import GST is 10% charged by the Australian Border Force on the customs value of imported goods (product cost + freight + insurance + duty). It is not the same as domestic GST — it is claimed through the deferred GST mechanism on your BAS, using the customs entry document as evidence rather than a supplier tax invoice.

Import GST is frequently miscoded in AP. When a freight forwarder invoice includes international freight (GST-free), customs duty (not GST), and import GST (deferred GST) on the same document, each line needs a different tax treatment. Processing the whole invoice under a single GST code produces errors on every import shipment. Use the customs duty and import GST calculator for import-specific calculations, and see the import GST coding guide for how to handle each component correctly.

Common GST mistakes in accounts payable

Five GST coding errors show up repeatedly in AP:

• Using × 10% instead of ÷ 11 to extract GST. This overstates the GST component and creates an incorrect input tax credit claim on the BAS.
• Applying GST to GST-free items. International freight, basic food, and medical supplies are GST-free. Claiming input tax credits on items that did not attract GST is a compliance risk.
• Coding import GST as standard GST. Import GST goes to a different BAS field (G20/1B) than domestic GST. Wrong coding means the ATO's cross-reference against border force records will not match.
• Not claiming GST on eligible expenses. Businesses that skip input tax credit claims because the invoice was coded incorrectly are leaving money with the ATO.
• Inconsistent GST treatment for the same supplier. When different people code the same supplier's invoices, they sometimes apply different GST treatments. Over a reporting period, this creates a reconciliation gap at BAS time.

For businesses processing more than 20 invoices a week, these errors compound. Automating accounts payable with line-level GST coding based on supplier history means the same supplier gets the same GST code every time.

GST and your BAS

GST collected on sales and GST paid on purchases flow directly into your Business Activity Statement. The key BAS labels:

• 1A — GST on sales: Total GST you collected from customers
• 1B — GST on purchases: Total GST you paid on business expenses (your input tax credit claim)
• G20 — Deferred import GST: Import GST claimed through the deferred scheme

Most small businesses lodge quarterly. Due dates are the 28th day after each quarter end: 28 October, 28 February, 28 April, and 28 July. Businesses with turnover over $20 million must lodge monthly. Late lodgement attracts a Failure to Lodge (FTL) penalty, and late payment accrues General Interest Charge (GIC) — currently around 11% per annum.

If your GST accounts in Xero or MYOB do not reconcile cleanly to your BAS labels, the problem is usually in how invoices were coded during the quarter. Use the BAS worksheet generator to prepare your figures before lodging, and review the BAS preparation and GST coding errors guide for the most common reconciliation issues.

Frequently asked questions

What is the difference between Add GST and Remove GST?

Add GST takes a net (ex-GST) amount and calculates the GST-inclusive price: net × 1.1. Remove GST takes a gross (GST-inclusive) amount and extracts the GST component: gross ÷ 11. Confusing the two is a frequent bookkeeping error that leads to overstating or understating GST credits on the BAS.

Can I claim GST on all my business purchases?

You can claim input tax credits on purchases that are used for your business and are not GST-free or input-taxed. You need a valid tax invoice from the supplier for amounts over $82.50 (including GST). For mixed-use purchases (partly personal, partly business), you can only claim the business portion. The ATO may audit GST credits, so keep supporting invoices for at least five years.

Is GST always 10% in Australia?

The GST rate in Australia is 10% with no reduced rates. Items are either taxable at 10%, GST-free at 0%, or input-taxed (no GST and no credits). This is simpler than the UK or EU VAT systems which have multiple rates, but it means the distinction between taxable and GST-free is critical — an item is either taxable or it is not.

What happens if I charge GST but I am not registered?

If you represent that a price includes GST without being GST-registered, you may be liable to pay the GST amount to the ATO regardless. The ATO can also impose penalties for misleading conduct. If you are not registered, your invoices should clearly state that the price does not include GST.

How often do I lodge a BAS and pay GST?

Most small businesses lodge quarterly, due on the 28th day after each quarter end (28 October, 28 February, 28 April, 28 July). Businesses with turnover over $20 million must lodge monthly. If you use a registered tax agent or BAS agent, you typically get an extended lodgement deadline. Late lodgement attracts a Failure to Lodge (FTL) penalty, and late payment accrues General Interest Charge (GIC) — currently around 11% per annum.

Can I use this calculator for New Zealand GST?

New Zealand GST is 15%, not 10%. Use the New Zealand GST calculator for NZ calculations.